Investment in Unconsolidated Affiliates Summarized Balance Sheet Information of Equity Method Investment (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Summarized Balance Sheet Information of Equity Method Investment [Abstract]
Current assets	$ 481.0	$ 416.0
Non-current assets	11,454.0	11,177.0
Current liabilities	1,403.0	1,279.0
Non-current liabilities	$ 2,964.0	$ 2,660.0

Summarized Balance Sheet Information of Equity Method Investment [Abstract]

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The amount of current assets reported by an equity method investment of the entity.

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